Nuclear fuel rod for fast reactors including metallic fuel slug coated with protective coating layer and fabrication method thereof

ABSTRACT

Provided are a nuclear fuel rod for fast reactors that includes a metallic fuel slug coated with a protective coating layer and a fabrication method thereof. The nuclear fuel rod for fast reactors that includes a surface treated metallic fuel slug and a cladding tube according to the present invention has an excellent effect of stabilizing components of the metallic fuel slug and fission products or impurities, because the interdiffusion between the metallic fuel slug and the cladding tube does not occur. Also, since the uniform coating on the surface of the metallic fuel slug may be facilitated and fabrication costs may be significantly reduced in comparison to a typical technique of using a functional material for preventing the interdiffusion at an inner surface of the cladding tube, it may be suitable for fabricating the nuclear fuel rod for fast reactors.

CROSS-REFERENCES TO RELATED APPLICATION

This patent application is a divisional application of U.S. applicationSer. No. 15/412,560, filed on Jan. 23, 2017, which is a continuationapplication of U.S. application Ser. No. 14/079,740, filed on Nov. 14,2013, now U.S. Pat. No. 9,589,680, issued Mar. 7, 2017, which claims thebenefit of priority from Korean Patent Application No. 10-2013-0005989filed on Jan. 18, 2013, and Korean Patent Application No.10-2013-0110624 filed on Sep. 13, 2013, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a nuclear fuel rod for fast reactorsthat includes a metallic fuel slug coated with a protective coatinglayer and a fabrication method thereof.

BACKGROUND

The present invention relates to a process for improving the performanceof nuclear fuel for reactors, and more particularly, to a technique thatstabilizes components of a metallic fuel slug and fission products orimpurities through the stabilization of surfaces of the metallic fuelslug and metallic fuel powder by a surface treatment.

Nuclear fuel in fast reactors is designed in various types, such as aplate type, a pellet type, and a rod type, and a fissionable materialthat undergoes a nuclear reaction is included in a nuclear fuel rod. Thefissionable material is sealed by a container, which is not reactive dueto its good compatibility with a coolant and has good heat transfercharacteristics, i.e. a cladding tube. The nuclear fuel rods beingmaintained at a constant spacing are assembled in the form of a fuelassembly and the assembly is charged into a nuclear reactor. In thiscase, the cladding tube surrounding the fuel must prevent chemicalinteractions between the fissionable material and the coolant byblocking a direct contact therebetween and must prevent the leakage offission products. In addition, in fast reactors using metallic nuclearfuel, it is highly advantageous in terms of the safety and economicefficiency of nuclear fuel to also inhibit interactions between thecladding tube and the fissionable material.

In particular, in fast reactors using metallic fuel, a phenomenonoccurs, in which a melting temperature of a metallic fuel slug decreasesor the strength of a cladding tube decreases by the interpenetrationbetween components (uranium (U), plutonium (Pu), thorium (Th), minoractinides (MA), zirconium (Zr), molybdenum (Mo), fission products, etc.)of the metallic fuel slug and components (iron (Fe), chromium (Cr),tungsten (W), Mo, vanadium (V), niobium (Nb), etc.) of the stainlesssteel cladding tube by diffusion. Thus, the maximum allowable bumup andthe maximum allowable operating temperature of the metallic fuel forfast reactors may be limited [J. Nucl. Mater., 204 (1993) p. 244-251 andJ. Nucl. Mater., 204 (1993) p. 141-147].

Also, a diffusion couple experiment performed at 923 K by T. Ogata etal. demonstrated the occurrence of a reaction due to the interdiffusionbetween a metallic fuel slug and a cladding tube, and reported that thethickness of an interaction layer increased proportional to the reactiontime [J. Nucl. Mater., 250 (1997) p. 171-175].

In order to prevent the interdiffusion reaction, General Electric (GE)disclosed a technique for inhibiting the interaction between a metallicfuel slug and a cladding tube by inserting an about 50 μm thick liner orsleeve formed of a metal of Zr, titanium (Ti), Nb, and Mo between themetallic fuel slug and the cladding tube.

Since the technique of GE essentially requires the introduction of anadditional process, the production of the nuclear fuel rod may not onlybe complicated, but considerable additional costs may also be required.

Also, in order to remove quartz tube mold waste generated during thepreparation of a fuel slug for fast reactors and simultaneously, toinhibit a fuel-cladding chemical interaction (FCCI) between metallicfuel slug and cladding tube, D. C. Crawford et al. melt-casted an about200 μm thick zirconium tube and reported the results of theirexperiments. However, cracks may occur in the zirconium tube.

Metallic fuel for reactors has been considered important as a nuclearfuel of sodium-cooled fast reactors, an advanced nuclear fuel, due tohigh thermal conductivity and high nuclear proliferation resistance inconjunction with pyroprocessing. However, with respect to the metallicfuel, since metallic uranium as a fuel material and a fuel claddingmaterial interdiffuse and react above 650° C., i.e., an operatingtemperature of the reactor, the thickness of a cladding tube decreasesaccording to the operating time. As a result, the lifetime of thecladding tube may decrease due to the deterioration of the soundnessthereof. In order to prevent the interaction phenomenon and improve theperformance of the cladding material, research into using a material forpreventing the interdiffusion and reaction between the fuel and thecladding tube has been conducted.

In Patent Document 1 (Korean Patent Application Laid-Open PublicationNo. KR-2009-0018396), a nuclear fuel rod for fast reactors, in which anoxide coating layer is formed on the inside of a cladding tube, issuggested in order to inhibit the fuel-cladding material interaction.Specifically, a concept of attaching chromium oxide, vanadium oxide, andzirconium oxide to the inside of the cladding tube by using an aciddissolution and oxidation method, a high-temperature oxidation method,an electrolytic oxidation method, and a vapor deposition method issuggested.

In Patent Document 2 (Korean Patent Application Laid-Open PublicationNo. KR-2010-0114392), a concept of depositing functional materials, suchas titanium, nickel, chromium, vanadium, and zirconium, in multilayersis suggested in order to inhibit the fuel-cladding material interactionand improve the performance of the fuel cladding tube.

In Patent Document 3 (Korean Patent Application Laid-Open PublicationNo. KR-2010-0081961), a method of uniformly plating an inner wall of afuel cladding tube and a concept of forming a nitride layer on a surfaceof the plating layer through an additional process of a nitridationtreatment are suggested.

In Patent Document 4 (Japanese Patent Application Laid-Open PublicationNo. 2012-237574), a typical main body that may accommodate nuclear fueland is formed of an iron-based material; and a cladding tube includingan inner layer part composed of a carbon-based material that is formedon an inner circumferential surface of the main body and a reactorincluding the cladding tube are suggested in order to provide a claddingtube that may improve high-temperature characteristics and powergeneration efficiency, and a reactor including the cladding tube.

However, the fuel cladding tube for fast reactors is a seamless tubehaving a diameter of 7 mm, a thickness of 0.6 mm, and a length of 3,000mm. Thus, there may be limitations in attaching the functional materialfor preventing interdiffusion to the inside of the thin and long tube,and treatment costs may be high.

Accordingly, the present inventors found that the interdiffusion betweena metallic fuel slug and a cladding tube may be prevented by stabilizingcomponents of the metallic fuel slug and fission products or impuritiesthough the simple and uniform formation of an oxide layer, a nitridelayer, or a carbide layer on the surface of the metallic fuel slug,thereby leading to completion of the present invention.

SUMMARY

One object of the present invention is to provide a metallic fuel slugcoated with a protective coating layer.

Another object of the present invention is to provide a nuclear fuel rodfor fast reactors including the metallic fuel slug.

Still another object of the present invention is to provide a method offabricating the nuclear fuel rod for fast reactors.

In order to achieve the object, the present invention provides ametallic fuel slug used in a nuclear fuel rod for fast reactors, themetallic fuel slug having a surface coated with a single protectivecoating layer selected from the group consisting of an oxide layer, anitride layer, and a carbide layer, wherein the protective coating layeris formed by oxidation, nitridation, or caburization of the metallicfuel slug.

The present invention also provides a nuclear fuel rod for fast reactorsincluding: a metallic fuel slug having a surface coated with a singleprotective coating layer selected from the group consisting of an oxidelayer, a nitride layer, and a carbide layer, wherein the protectivecoating layer is formed by oxidation, nitridation, or caburization ofthe metallic fuel slug; and a cladding tube sealing the metal fuel slug.

Furthermore, the present invention provides a method of fabricating anuclear fuel rod for fast reactors including: coating a surface of ametallic fuel slug with a single protective coating layer selected fromthe group consisting of an oxide layer, a nitride layer, and a carbidelayer by oxidation, nitridation, or caburization of the metallic fuelslug (step 1); and sealing a cladding tube after introducing themetallic fuel slug coated with the protective coating layer in step 1into the cladding tube (step 2).

The present invention also provides a method of fabricating a nuclearfuel rod for fast reactors including: coating a surface of metallic fuelpowder with a single protective coating layer selected from the groupconsisting of an oxide layer, a nitride layer, and a carbide layer byoxidation, nitridation, or caburization of the metallic fuel powder(step 1); preparing a metallic fuel slug by forming the metallic fuelpowder coated with the protective coating layer in step 1 (step 2); andsealing a cladding tube after introducing the metallic fuel slugprepared in step 2 into the cladding tube (step 3).

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic view illustrating a metallic fuel slug coated witha protective coating layer according to the present invention;

FIG. 2 is a scanning electron microscope image of a cross section of anuclear fuel rod for fast reactors according to Example 1 of the presentinvention after a diffusion couple experiment;

FIG. 3 is a scanning electron microscope image of a cross section of anuclear fuel rod for fast reactors according to Example 2 of the presentinvention after a diffusion couple experiment;

FIG. 4 is a scanning electron microscope image of a cross section of anuclear fuel rod for fast reactors according to Example 3 of the presentinvention after a diffusion couple experiment;

FIG. 5 is a scanning electron microscope image of a cross section of anuclear fuel rod for fast reactors according to Example 18 of thepresent invention after a diffusion couple experiment; and

FIG. 6 is a scanning electron microscope image of a cross section of anuclear fuel rod for fast reactors according to Comparative Example 1 ofthe present invention after a diffusion couple experiment.

DETAILED DESCRIPTION

Features and advantages of the present invention will be more clearlyunderstood by the following detailed description of the presentpreferred embodiments by reference to the accompanying drawings. It isfirst noted that terms or words used herein should be construed asmeanings or concepts corresponding with the technical sprit of thepresent invention, based on the principle that the inventor canappropriately define the concepts of the terms to best describe his owninvention. Also, it should be understood that detailed descriptions ofwell-known functions and structures related to the present inventionwill be omitted so as not to unnecessarily obscure the important pointof the present invention.

Hereinafter, the present invention will be described in detail.

The present invention provides a metallic fuel slug used in a nuclearfuel rod for fast reactors, the metallic fuel slug having a surfacecoated with a single protective coating layer selected from the groupconsisting of an oxide layer, a nitride layer, and a carbide layer,wherein the protective coating layer is formed by oxidation,nitridation, or caburization of the metallic fuel slug.

In the metallic fuel slug coated with a protective coating layeraccording to the present invention, since components of the metallicfuel slug, fission products, or impurities are stabilized, aninterdiffusion phenomenon occurred between the metallic fuel slug andthe cladding tube sealing the metallic fuel slug during the fabricationof the nuclear fuel rod for fast reactors may be reduced. Also,according to the present invention, since a rare earth element, which isincluded on the surface of a metallic fuel fabricated by pyroprocessingto degrade the performance of the metallic fuel, may be transformed intoa non-active compound, such as oxide, nitride, and carbide, theperformance of the metallic fuel may be improved.

With respect to the metallic fuel slug according to the presentinvention, the metallic fuel slug may be fabricated by including uranium(U), plutonium (Pu), thorium (Th), minor actinides (MA, neptunium (Np),americium (Am), and curium (Cm)), rare earth elements (RE, lanthanum(La), cerium (Ce), neodymium (Nd), praseodymium (Pr), promethium (Pm),samarium (Sm), europium (Eu), and gadolinium (Gd)), zirconium (Zr), andmolybdenum (Mo) alone or in a mixture thereof. However, any metallicfuel slug applicable to the nuclear fuel rod for fast reactors may beused.

With respect to the metallic fuel slug according to the presentinvention, a thickness of the protective coating layer may be in a rangeof 0.5 μm to 100 μm.

In the case that the thickness of the protective coating layer is lessthan 0.5 μm, the interdiffusion phenomenon may not be sufficientlyinhibited. In the case in which the thickness of the protective coatinglayer is greater than 100 μm, since thermal conductivity may decreasedue to the thick coating layer, heat discharged from the fuel may not beefficiently transferred.

The present invention also provides a nuclear fuel rod for fast reactorsincluding a metallic fuel slug having a surface coated with a singleprotective coating layer selected from the group consisting of an oxidelayer, a nitride layer, and a carbide layer, wherein the protectivecoating layer is formed by oxidation, nitridation, or caburization ofthe metallic fuel slug; and a cladding tube sealing the metal fuel slug.

With respect to the nuclear fuel rod for fast reactors according to thepresent invention, the metallic fuel slug may be fabricated by includingU, Pu, Th, MA (Np, Am, and Cm), RE (La, Ce, Nd, Pr, Pm, Sm, Eu, and Gd),Zr, and Mo alone or in a mixture thereof. However, any metallic fuelslug applicable to the nuclear fuel rod for fast reactors may be used.

With respect to the nuclear fuel rod for fast reactors according to thepresent invention, a thickness of the protective coating layer may be ina range of 0.5 μm to 100 μm.

In the case that the thickness of the protective coating layer is lessthan 0.5 μm, the interdiffusion phenomenon may not be sufficientlyinhibited. In the case in which the thickness of the protective coatinglayer is greater than 100 μm, since thermal conductivity may decreasedue to the thick coating layer, heat discharged from the fuel may not beefficiently transferred.

With respect to the nuclear fuel rod for fast reactors according to thepresent invention, the cladding tube may include iron (Fe), chromium(Cr), tungsten (W), Mo, vanadium (V), titanium (Ti), niobium (Nb),tantalum (Ta), silicon (Si), manganese (Mn), nickel (Ni), carbon (C),nitrogen (N), and boron (B) alone or in the form of an alloy by mixingthereof. However, the present invention is not limited thereto.

Furthermore, the present invention provides a method of fabricating anuclear fuel rod for fast reactors including: coating a surface of ametallic fuel slug with a single protective coating layer selected fromthe group consisting of an oxide layer, a nitride layer, and a carbidelayer by oxidation, nitridation, or caburization of the metallic fuelslug (step 1); and sealing a cladding tube after introducing themetallic fuel slug coated with the protective coating layer in step 1into the cladding tube (step 2).

In the fabricating method according to the present invention, step 1 isa step of forming the protective coating layer on the surface of themetallic fuel slug. Specifically, an oxide, nitride, or carbide coatinglayer may be formed on the surface of the metallic fuel slug byoxidation, nitridation, or caburization of the metallic fuel slug.

In the fabricating method according to the present invention, step 2 isa step of sealing the cladding tube after introducing thesurface-treated metallic fuel slug into the cladding tube.

Formation of Oxide Protective Coating Layer

A method of heat treating in a gas atmosphere containing oxygen, amethod of dipping in an oxidation solution, and a method of performingan electrolytic treatment may be used as a method of forming an oxideprotective coating layer.

First, the method of heat treating in a gas atmosphere containing oxygenmay be performed by heat treating a metallic fuel slug at a temperatureranging from 100° C. to 1000° C. and a pressure ranging from 1 atm to 50atm in an atmosphere of oxygen, air, or inert gas containing oxygen.

In the case that the heat treatment temperature is less than 100° C.,the oxide layer may not be efficiently formed. In the case in which theheat treatment temperature is greater than 1000° C., transformation ofthe metallic fuel slug may occur and thus, the performance of themetallic fuel slug as a fuel may be degraded. Also, a pressurizationtreatment may be performed for the efficient heat treatment. In the casethat the pressure of the heat treatment is 50 atm or more, an additionalsealing apparatus may be required, and thus, economic efficiency of theprocess may be reduced.

Next, the method of dipping in an oxidation solution may be performed bydipping a metallic fuel slug in a hydrochloric, sulfuric, nitric, sodiumhydroxide, or potassium hydroxide solution, and heat treating themetallic fuel slug at a temperature ranging from 30° C. to 90° C. for 30minutes to 5 hours.

Finally, the method of performing an electrolytic treatment may beperformed by plasma electrolytic oxidation, micro-arc oxidation,micro-arc discharge oxidation, spark anodizing, anodic spark deposition,micro-arc anodizing, micro plasma anodizing, micro plasma oxidation, andelectro plasma oxidation of a metallic fuel slug.

Formation of Nitride Protective Coating Layer

A method of heat treating in a gas atmosphere containing nitrogen and anion nitriding method may be used as a method of forming a nitrideprotective coating layer.

First, the method of heat treating in a gas atmosphere containingnitrogen may be performed by heat treating a metallic fuel slug at atemperature ranging from 100° C. to 1000° C. and a pressure ranging from1 atm to 50 atm in an atmosphere of nitrogen, ammonia, or inert gascontaining nitrogen.

In the case that the heat treatment temperature is less than 100° C.,the nitride layer may not be efficiently formed. In the case in whichthe heat treatment temperature is greater than 1000° C., transformationof the metallic fuel slug may occur and thus, the performance of themetallic fuel slug as a fuel may be degraded. Also, a pressurizationtreatment may be performed for the efficient heat treatment. In the casethat the pressure of the heat treatment is 50 atm or more, an additionalsealing apparatus may be required, and thus, economic efficiency of theprocess may be reduced.

Next, the ion nitriding method may be performed by using a method ofapplying a negative potential to an object to be ion-nitrided in a gasatmosphere containing nitrogen. The ion nitriding method may becompleted by heat treating the object under conditions of a temperatureranging from 100° C. to 1000° C., a pressure ranging from 1 atm to 50atm, and a potential ranging from 1 V to 1,000 V in an inert atmospherecontaining nitrogen. In the case that the heat treatment temperature isless than 100° C., the nitride layer may not be efficiently formed. Inthe case in which the heat treatment temperature is greater than 1000°C., transformation of the metallic fuel slug may occur and thus, theperformance of the metallic fuel slug as a fuel may be degraded. Also, apressurization treatment may be performed for the efficient heattreatment. In the case that the pressure of the heat treatment is 50 atmor more, an additional sealing apparatus may be required, and thus,economic efficiency of the process may be reduced. With respect to theapplied potential, efficient ion nitridation may not be achieved at apotential of less than 1 V. Since an additional insulation treatment maybe required at a potential of greater than 1,000 V, economic efficiencyof the process may be reduced.

Formation of Carbide Protective Coating Layer

A method of heat treating in a gas atmosphere containing carbon may beused as a method of forming a carbide protective coating layer.

The method of heat treating in a gas atmosphere containing carbon may beperformed by heat treating a metallic fuel slug at a temperature rangingfrom 100° C. to 1000° C. and a pressure ranging from 1 atm to 50 atm inan atmosphere of carbon, methane, carbon dioxide, or carbon monoxide.

In the case that the heat treatment temperature is less than 100° C.,the carbide layer may not be efficiently formed. In the case in whichthe heat treatment temperature is greater than 1000° C., transformationof the metallic fuel slug may occur and thus, the performance of themetallic fuel slug as a fuel may be degraded. Also, a pressurizationtreatment may be performed for the efficient heat treatment. In the casethat the pressure of the heat treatment is 50 atm or more, an additionalsealing apparatus may be required, and thus, economic efficiency of theprocess may be reduced.

Also, the present invention provides a method of fabricating a nuclearfuel rod for fast reactors including: coating a surface of metallic fuelpowder with a single protective coating layer selected from the groupconsisting of an oxide layer, a nitride layer, and a carbide layer byoxidation, nitridation, or caburization of the metallic fuel powder(step 1); preparing a metallic fuel slug by forming the metallic fuelpowder coated with the protective coating layer in step 1 (step 2); andsealing a cladding tube after introducing the metallic fuel slugprepared in step 2 into the cladding tube (step 3).

Since the method of fabricating a nuclear fuel rod for fast reactorsaccording to the present invention may form the protective coating layeron the surface of the metallic fuel powder, components of fuel, fissionproducts, or impurities may be stabilized and various types of fuels maybe fabricated. In particular, the coated metallic fuel powder may beformed in the form of a metallic fuel slug during the fabrication of thenuclear fuel rod for fast reactors and thus, the interdiffusionphenomenon between the metallic fuel slug and the cladding tube sealingthe metallic fuel slug may be reduced.

In the fabricating method according to the present invention, step 1 isa step of forming the protective coating layer on the surface of themetallic fuel powder. Specifically, an oxide, nitride, or carbidecoating layer may be formed on the surface of the metallic fuel powderby oxidation, nitridation, or caburization of the metallic fuel powder.Preferred conditions that may form the protective layers are asdescribed in the above specification.

In the fabricating method according to the present invention, step 2 isa step of preparing the metallic fuel slug by forming the metallic fuelpowder. Specifically, a method of stacking the powder in a nuclear fuelrod composed of a cylindrical cladding tube, a method of sintering thepowder by heat treating in a heat treatment furnace, and a method offorming a cylindrical sintered body by introducing the metallic fuelpowder into a metal or ceramic matrix and heat treating.

In the fabricating method according to the present invention, step 3 isa step of sealing the cladding tube after introducing the metallic fuelslug into the cladding tube.

As described above, the nuclear fuel rod for fast reactors that includesthe surface treated metallic fuel slug and the cladding tube accordingto the present invention has an excellent effect of stabilizingcomponents of the metallic fuel slug and fission products or impurities,because the interdiffusion between the metallic fuel slug and thecladding tube does not occur. Also, since the uniform coating on thesurface of the metallic fuel slug may be facilitated and fabricationcosts may be significantly reduced in comparison to a typical techniqueof using a functional material for preventing the interdiffusion at aninner surface of the cladding tube, it may be suitable for fabricatingthe nuclear fuel rod for fast reactors.

Hereinafter, the present invention will be described in more detailaccording to examples. However, the following examples are provided forillustrative purposes only, and the scope of the present inventionshould not be limited thereto in any manner.

<Example 1> Fabrication 1 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 600° C. and a pressure of 5 atm for 2hours in an argon gas atmosphere containing 20% oxygen. Then, theheat-treated metallic fuel slug was put into a HT9 (12Cr-1Mo) claddingtube to fabricate a nuclear fuel rod for fast reactors.

<Example 2> Fabrication 2 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 150° C. and a pressure of 1 atm for 1 hourin an air atmosphere. Then, the heat-treated metallic fuel slug was putinto a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod forfast reactors.

<Example 3> Fabrication 3 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 300° C. and a pressure of 1 atm for 1 hourin an air atmosphere. Then, the heat-treated metallic fuel slug was putinto a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod forfast reactors.

<Example 4> Fabrication 4 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bydipping the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, in a hydrochloric acid solution at 50° C. for 2 hours. Then,the metallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 5> Fabrication 5 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bydipping the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, in a sulfuric acid solution at 50° C. for 2 hours. Then, themetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 6> Fabrication 6 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bydipping the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, in a nitric acid solution at 50° C. for 2 hours. Then, themetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 7> Fabrication 7 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bydipping the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, in a sodium hydroxide solution at 50° C. for 2 hours. Then,the metallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 8> Fabrication 8 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bydipping the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, in a potassium hydroxide solution at 50° C. for 2 hours. Then,the metallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 9> Fabrication 9 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug throughplasma electrolytic oxidation by dipping the metallic fuel slug formedof U-10Zr, a nuclear fuel material, in a potassium hydroxide solutionand a sodium hydroxide solution, and then applying a positive voltage of200 V thereto. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 10> Fabrication 10 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bymicro-arc oxidation of the metallic fuel slug formed of U-10Zr, anuclear fuel material. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 11> Fabrication 11 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bymicro-arc discharge oxidation of the metallic fuel slug formed ofU-10Zr, a nuclear fuel material. Then, the metallic fuel slug was putinto a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod forfast reactors.

<Example 12> Fabrication 12 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by sparkanodizing of the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial. Then, the metallic fuel slug was put into a HT9 (12Cr-1Mo)cladding tube to fabricate a nuclear fuel rod for fast reactors.

<Example 13> Fabrication 13 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by anodicspark deposition of the metallic fuel slug formed of U-10Zr, a nuclearfuel material. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 14> Fabrication 14 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug bymicro-arc anodizing of the metallic fuel slug formed of U-10Zr, anuclear fuel material. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 15> Fabrication 15 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by microplasma anodizing of the metallic fuel slug formed of U-10Zr, a nuclearfuel material. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 16> Fabrication 16 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug by microplasma oxidation of the metallic fuel slug formed of U-10Zr, a nuclearfuel material. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 17> Fabrication 17 of Nuclear Fuel Rod for Fast Reactors HavingOxide Layer Formed on Surface

An oxide layer was formed on a surface of a metallic fuel slug byelectro plasma oxidation of the metallic fuel slug formed of U-10Zr, anuclear fuel material. Then, the metallic fuel slug was put into a HT9(12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Example 18> Fabrication 1 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

A nitride layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 800° C. and a pressure of 2 atm for 2hours in a 100% pure ammonia gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 19> Fabrication 2 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

A nitride layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 500° C. and a pressure of 2 atm for 2hours in a 100% pure ammonia gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 20> Fabrication 3 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

A nitride layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 300° C. and a pressure of 2 atm for 2hours in a 100% pure ammonia gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 21> Fabrication 4 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

A nitride layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 150° C. and a pressure of 2 atm for 2hours in a 100% pure ammonia gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 22> Fabrication 5 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

An ion-nitrided layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into a mixed gas containing 80% nitrogen and 20% argon gas,and heat treating the metallic fuel slug at a temperature of 800° C. anda negative voltage of 200 V for 2 hours. Then, the metallic fuel slugwas put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuelrod for fast reactors.

<Example 23> Fabrication 6 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

An ion-nitrided layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into a mixed gas containing 80% nitrogen and 20% argon gas,and heat treating the metallic fuel slug at a temperature of 500° C. anda negative voltage of 200 V for 2 hours. Then, the metallic fuel slugwas put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuelrod for fast reactors.

<Example 24> Fabrication 7 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

An ion-nitrided layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into a mixed gas containing 80% nitrogen and 20% argon gas,and heat treating the metallic fuel slug at a temperature of 300° C. anda negative voltage of 200 V for 2 hours. Then, the metallic fuel slugwas put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuelrod for fast reactors.

<Example 25> Fabrication 8 of Nuclear Fuel Rod for Fast Reactors HavingNitride Layer Formed on Surface

An ion-nitrided layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into a mixed gas containing 80% nitrogen and 20% argon gas,and heat treating the metallic fuel slug at a temperature of 150° C. anda negative voltage of 200 V for 2 hours. Then, the metallic fuel slugwas put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuelrod for fast reactors.

<Example 26> Fabrication 1 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into carbon powder and heat treating the metallic fuel slug ata temperature of 700° C. and a pressure of 1 atm for 2 hours. Then, theheat-treated metallic fuel slug was put into a HT9 (12Cr-1Mo) claddingtube to fabricate a nuclear fuel rod for fast reactors.

<Example 27> Fabrication 2 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into carbon powder and heat treating the metallic fuel slug ata temperature of 500° C. and a pressure of 1 atm for 2 hours. Then, theheat-treated metallic fuel slug was put into a HT9 (12Cr-1Mo) claddingtube to fabricate a nuclear fuel rod for fast reactors.

<Example 28> Fabrication 3 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into carbon powder and heat treating the metallic fuel slug ata temperature of 300° C. and a pressure of 1 atm for 2 hours. Then, theheat-treated metallic fuel slug was put into a HT9 (12Cr-1Mo) claddingtube to fabricate a nuclear fuel rod for fast reactors.

<Example 29> Fabrication 4 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug byintroducing the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, into carbon powder and heat treating the metallic fuel slug ata temperature of 150° C. and a pressure of 1 atm for 2 hours. Then, theheat-treated metallic fuel slug was put into a HT9 (12Cr-1Mo) claddingtube to fabricate a nuclear fuel rod for fast reactors.

<Example 30> Fabrication 5 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 700° C. and a pressure of 1 atm for 2hours in a methane gas atmosphere. Then, the heat-treated metallic fuelslug was put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclearfuel rod for fast reactors.

<Example 31> Fabrication 6 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 500° C. and a pressure of 1 atm for 2hours in a methane gas atmosphere. Then, the heat-treated metallic fuelslug was put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclearfuel rod for fast reactors.

<Example 32> Fabrication 7 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 300° C. and a pressure of 1 atm for 2hours in a methane gas atmosphere. Then, the heat-treated metallic fuelslug was put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclearfuel rod for fast reactors.

<Example 33> Fabrication 8 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 150° C. and a pressure of 1 atm for 2hours in a methane gas atmosphere. Then, the heat-treated metallic fuelslug was put into a HT9 (12Cr-1Mo) cladding tube to fabricate a nuclearfuel rod for fast reactors.

<Example 34> Fabrication 9 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 700° C. and a pressure of 1 atm for 2hours in a carbon dioxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 35> Fabrication 10 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 500° C. and a pressure of 1 atm for 2hours in a carbon dioxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 36> Fabrication 11 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 300° C. and a pressure of 1 atm for 2hours in a carbon dioxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 37> Fabrication 12 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 150° C. and a pressure of 1 atm for 2hours in a carbon dioxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 38> Fabrication 13 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 700° C. and a pressure of 1 atm for 2hours in a carbon monoxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 39> Fabrication 14 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 500° C. and a pressure of 1 atm for 2hours in a carbon monoxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 40> Fabrication 15 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 300° C. and a pressure of 1 atm for 2hours in a carbon monoxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Example 41> Fabrication 16 of Nuclear Fuel Rod for Fast Reactors HavingCarbide Layer Formed on Surface

A carbide layer was formed on a surface of a metallic fuel slug by heattreating the metallic fuel slug formed of U-10Zr, a nuclear fuelmaterial, at a temperature of 150° C. and a pressure of 1 atm for 2hours in a carbon monoxide gas atmosphere. Then, the heat-treatedmetallic fuel slug was put into a HT9 (12Cr-1Mo) cladding tube tofabricate a nuclear fuel rod for fast reactors.

<Comparative Example 1> Fabrication of Nuclear Fuel Rod for FastReactors with No Surface Treatment

A surface treatment was not performed on a metallic fuel slug formed ofU-10Zr, a nuclear fuel material, and the metallic fuel slug was put intoa HT9 (12Cr-1Mo) cladding tube to fabricate a nuclear fuel rod for fastreactors.

<Experimental Example 1> Metallic Fuel Slug-Cladding Tube DiffusionCouple Experiment

The following experiments were performed for evaluating theinterdiffusivity between the metallic fuel slug and the cladding tube inthe nuclear fuel rods for fast reactors fabricated in examples.

Specifically, the nuclear fuel rods for fast reactors fabricated inExamples 1, 2, 3, and 18, and Comparative Example 1 were cut to a lengthof 10 mm, and the 10 mm long nuclear fuel rods were then cut in half ina radial direction. Then, metallic fuel slug-cladding tube diffusioncouple experiments were performed at 800° C. for 25 hours. After thediffusion couple experiments, bonded samples were cooled and crosssections of the bonded samples were observed using a scanning electronmicroscope. The results thereof are presented in FIGS. 2 to 6.

FIG. 2 is a scanning electron microscope image of the cross section ofthe nuclear fuel rod for fast reactors according to Example 1 of thepresent invention after the diffusion couple experiment.

FIG. 3 is a scanning electron microscope image of the cross section ofthe nuclear fuel rod for fast reactors according to Example 2 of thepresent invention after the diffusion couple experiment.

FIG. 4 is a scanning electron microscope image of the cross section ofthe nuclear fuel rod for fast reactors according to Example 3 of thepresent invention after the diffusion couple experiment.

FIG. 5 is a scanning electron microscope image of the cross section ofthe nuclear fuel rod for fast reactors according to Example 18 of thepresent invention after the diffusion couple experiment.

FIG. 6 is a scanning electron microscope image of the cross section ofthe nuclear fuel rod for fast reactors according to Comparative Example1 of the present invention after the diffusion couple experiment.

As illustrated in FIGS. 2 to 6, with respect to Example 1 (FIG. 2),Example 2 (FIG. 3), Example 3 (FIG. 4), and Example 18 (FIG. 5), it wasobserved that the interactions between the metallic fuel slugs and thecladding tubes did not occur because dense oxide layers and nitridelayer were formed on the surfaces of the metallic fuel slugs. Incontrast, with respect to Comparative Example 1 (FIG. 6), it may beobserved that the metallic fuel slug material and the cladding tubematerial were interdiffused and reacted during the diffusion coupleexperiment.

Therefore, the nuclear fuel rod for fast reactors that includes thesurface treated metallic fuel slug and the cladding tube according tothe present invention had an excellent effect of stabilizing componentsof the metallic fuel slug and fission products or impurities, becausethe interdiffusion between the metallic fuel slug and the cladding tubedid not occur. Also, since the uniform coating on the surface of themetallic fuel slug may be facilitated and fabrication costs may besignificantly reduced in comparison to a typical technique of using afunctional material for preventing the interdiffusion at an innersurface of the cladding tube, it may be suitable for fabricating thenuclear fuel rod for fast reactors. Furthermore, according to thepresent invention, since a rare earth element, which is included on thesurface of a metallic fuel fabricated by pyroprocessing to degrade theperformance of the metallic fuel, may be transformed into a non-activecompound, such as oxide, nitride, and carbide, the improvement of theperformance of the metallic fuel and the extension of the lifetime ofthe metallic fuel may be expected.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A fast reactor nuclear fuel element comprising: ametallic fuel slug, the fuel slug consisting essentially of a uranium(U) and zirconium (Zr) alloy; a protective coating layer of a nitridelayer or a carbide layer, the protective coating layer is coated on asurface of the fuel slug, which causes the fuel slug to be coated withthe single protective coating layer of the nitride layer or the carbidelayer, the single protective coating layer is formed by nitridation orcaburization of the fuel slug, thickness of the single protectivecoating layer is in a range of 0.5 μm to 100 μm, and the singleprotective coating layer is preformed on the fuel slug surface prior tofuel slug usage in a fast reactor, the single protective coating layeris configured to prevent interdiffusion between the fuel slug and acladding tube, to prevent the cladding tube from thinning during fissionoperation in the fast reactor.
 2. A nuclear fuel rod configured for usewith a fast reactor comprising: a fast reactor nuclear fuel element ofclaim 1; and a cladding tube sealing the metal fuel slug.
 3. The nuclearfuel rod as set forth in claim 2, wherein the cladding tube comprisesone or more selected from the group consisting of iron (Fe), chromium(Cr), tungsten (W), molybdenum (Mo), vanadium (V), titanium (Ti),niobium (Nb), tantalum (Ta), silicon (Si), manganese (Mn), nickel (Ni),carbon (C), nitrogen (N), and boron (B).